The present invention relates to power tools and in particular to a digital read-out device that is adapted to automatically provide a precise digital reading of the depth adjustment of the blade of the tool.
Hand tools such as routers and circular saws, typically have mechanisms for adjusting the cutting depth of the blade of the tool. However, obtaining a desired cutting depth is often a time consuming task in that it generally involves a trial and error process as the user cuts a sample piece of stock, measures the resulting cutting depth, and then attempts to make the appropriate corrective adjustment. In addition, it is cumbersome to make a precise depth adjustment utilizing the mechanical vernier type adjustment mechanisms found on most tools, especially when limited to the trial and error method of adjustment.
Accordingly, it is the primary object of the present invention to provide a tool having an electronic depth measuring device that is capable of providing a precise digital read-out of the depth adjustment of the blade of the tool. In general, this is accomplished through the use of a microprocessor that drives a digital display. The microprocessor receives position information from an encoder that is coupled to the blade adjusting mechanism of the tool. In the preferred embodiment herein the encoder comprises a 52-position, two-channel gray code switch that is mechanically coupled to the shaft incorporating the pinion gear of a rack and pinion adjustment mechanism. However, it is to be understood that the use of other types of position encoders is contemplated and within the scope of the present invention.
In addition, the preferred embodiment of the present invention includes the novel feature of an automatically inverting digital display which permits the operator to readily read the display when adjustments are made while the tool is upside-down, which is sometimes convenient, particularly with a router. In general, this is accomplished by programming the microprocessor to interrogate the condition of a single-pole mercury switch whose state is affected by the orientation of the tool, and then control the orientation of the digital display accordingly.
Also included in the preferred embodiment herein is a mode select capability which permits the operator to select between either an English or Metric units read-out, and a reset capability that allows the operator to readily obtain an accurate depth adjustment relative to any other preselected depth setting.